Feedback linking cell envelope stiffness, curvature, and synthesis enables robust rod-shaped bacterial growth

Bacterial growth is remarkably robust to environmental fluctuations, yet the mecha-nisms of growth-rate homeostasis are poorly understood. Here, we combine theory and experiment to infer mechanisms by which Escherichia coli adapts its growth rate in response to changes in osmolarity, a fundamental physicochemical property of the envi-ronment. The central tenet of our theoretical model is that cell-envelope expansion is only sensitive to local information, such as enzyme concentrations, cell-envelope curva-ture, and mechanical strain in the envelope. We constrained this model with quantita-tive measurements of the dynamics of E. coli elongation rate and cell width after hyperosmotic shock. Our analysis demonstrated that adaptive cell-envelope softening is a key process underlying growth-rate homeostasis. Furthermore, our model correctly predicted that softening does not occur above a critical hyperosmotic shock magnitude and precisely recapitulated the elongation-rate dynamics in response to shocks with magnitude larger than this threshold. Finally, we found that, to coordinately achieve growth-rate and cell-width homeostasis, cells employ direct feedback between cell -envelope curvature and envelope expansion. In sum, our analysis points to cellular mechanisms of bacterial growth-rate homeostasis and provides a practical theoretical framework for understanding this process.

Automated summary

The growth rate of bacteria can adapt to environmental fluctuations through the softening of the cell envelope. This adaptation is only sensitive to local information such as enzyme concentrations and cell envelope curvature. It was also found that the softening of the cell envelope does not occur above a certain magnitude of osmotic shock, and there is direct feedback between cell envelope curvature and envelope expansion.